Digital wireless communications are being widely used throughout the world particularly with the latest development of the Orthogonal Frequency Division Multiplex (OFDM systems) and the last evolution, namely the so-called Long Term Evolution (LTE) systems.
When a User Equipment (UE) wishes to access an LTE network, it must initiate a cell search procedure consisting of a series of synchronization steps by which the UE determines time and frequency parameters particularly necessary for the purpose of demodulating the downlink and also for getting critical system parameters.
In LTE, the cell search procedure is based on the use of two particular synchronization signals being broadcast in each cell, namely the so-called Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS).
The synchronization signals (PSS and SSS) are sequences of length 62 which are mapped to the central 62 sub-carriers (not including the d.c.) independently of the transmission bandwidth, as illustrated in FIG. 1.
Generally speaking, in LTE, the largest unit of time is the 10 ms radio frame, which is subdivided into ten 1 ms subframes, each of which being split into two 0.5 ms slots. Each slot comprises six to seven OFDM symbols in accordance with the length of the cyclic prefix. In the frequency domain, resources are grouped in units of 12 subcarriers and each block of 12 subcarriers, during one slot, is called a Resource Block (RB), the latter being divided into Resources Elements (RE) which lasts for one OFDM symbol.
The reader is invited to refer to the literature regarding LTE, and particularly to the following document:    “LTE—The UMTS Long Term Evolution: from Theory to Practice” by SESIA Stefania, TOUFIK Issam, BAKER Mattew, Wiley, 2009.
FIG. 2, recalls the general structure of the LTE sub-frame comprising both the broadcasted PSS and SSS signals.
As known by the skilled man, in order to synchronize, the UE has first to detect the PSS, which detection is then used for the purpose of the decoding of the SSS which provides the identification of the cell, such subsequent extraction being further required for the purpose of the decoding of the pilots or Reference Signals necessary for getting critical system parameters and also for achieving an accurate estimation of the channel.
While the decoding of the pilot signals allow the estimation of the channel, it may be useful that such channel estimation be allowable as soon as possible, and particularly during the first phase of the synchronization, at the extraction of the PSS.
Such channel estimation is highly desirable since it significantly improves the efficiency of the subsequent synchronization phases; In particular, the knowledge of the channel allows the designer the possibility to consider coherent SSS detection methods which are known to be more efficient.
It is therefore desirable to keep the channel estimation procedure as simple as possible in order to reduce complexity and the amount of digital processing resources required.
Such is the technical problem to solve by the present invention.